The performance of electric batteries installed in vehicles for driving the vehicles varies depending on the environmental temperature in use. For example, the charging-discharging efficiency of electric batteries at low temperature is lower than that at ordinary temperature. Cases for the electric batteries thus include thermosensors in addition to electric heaters to maintain the temperature of the batteries within a predetermined range.
In hybrid vehicles including motors for driving the vehicles by both the power from generators driven by engines and the power charged in electric batteries, the motors can be driven by the generated power alone even if at low battery temperature. Conventional controlling apparatuses warm electric batteries while driving vehicles by the power from generators.
For example, a typical controlling apparatus warms an electric battery while driving a vehicle through the supply of generated power to an electric heater and a motor. Alternatively, the electric battery may be warmed by the Joule heat generated during the charge-discharge cycles of the electric battery (refer to Japanese Unexamined Patent Application Publication No. 2012-214142). These techniques enable ensuring of the driving stability of the vehicle and warm-up of the electric battery at the same time.
Unfortunately, the charging-discharging characteristics of the electric battery significantly deteriorate, for example, at a cryogenic temperature (deep freeze temperature) substantially below 0° C. In particular, the characteristics rapidly deteriorate during a charging operation. The electric battery repeatedly charged and discharged at significantly low temperature may have a decreased service life. Furthermore, the electric battery in the running vehicle may be unintentionally charged with the power regenerated by the motor regardless of the standby mode of the generator. Eagerly anticipated is a controlling apparatus to control power not to flow to the electric battery while the vehicle is being driven.
The deterioration of the cold electric battery can be prevented through the electrical disconnection of the electric battery from an electric circuit for avoiding the charge-discharge of the electric battery. Unfortunately, the disconnection of the electric battery from the electric circuit cannot provide a buffering effect (effect of reducing fluctuations in the voltage) . In other words, the fluctuations in load directly affect a converter or an inverter in the electric circuit, resulting in an error in their operations.